PBR Textures; can I mix them with basic MS.Paint images?
There are a couple of ways you can mix them. The way I would suggest is to keep your PBR material setup connected to the Principled BSDF, and then run your MSPAINT image through a Diffuse BSDF and mix the two using a Mix Shader.

As you can see from the image, I mixed them using a converted Black and White version of the original image as a mix factor. This is in the case you don't have a mask for your MSPAINT image (if needed), you can create one using a RGB to BW node and a ColorRamp.

Another way you can do this (which is handy if you only want to mix BaseColors, but have the rest of the PBR properties &quot;apply&quot; to your mixed image) is to mix the BaseColor texture of your PBR set with your MSPAINT image (using the same mix factor methodd, if desired) using a MixRGB node: